1. Field of the Invention
The present invention relates to a curable silicone emulsion composition, and relates particularly to an addition reaction-curable silicone emulsion composition for release applications that exhibits excellent curability with a small amount of platinum.
2. Description of the Prior Art
Silicone release compositions have conventionally been used to prevent tack or adhesion between substrates such as papers or plastic films and pressure-sensitive adhesive materials. One known form of this type of silicone release composition is an emulsior-type silicone composition, and the mode of curing for these emulsion-type silicone compositions involves either condensation reaction curing or addition reaction curing.
Of these emulsion-type silicone compositions, the condensation reaction-curable silicone compositions suffer from an extremely short pot life, and are therefore only used in very specific applications. On the other hand, examples of addition reaction-curable silicone compositions that have been proposed include silicone release compositions that are produced by mixing two types of emulsions (see Patent Document 1), release paper compositions that are produced using an emulsion polymerization method (see Patent Document 2), and compositions that employ two liquid catalysts (see Patent Document 3).
However, each of these patented compositions also has drawbacks. In the case of a silicone release composition that is produced by mixing two types of emulsions, because the composition is produced by mixing, the curing rate of the composition obtained following mixing tends to be slow.
In the case of a release paper composition that is produced using an emulsion polymerization method, the properties of the resulting composition are still inferior to those of a composition obtained using a mechanical emulsion method, and the peel strength also tends to be relatively high.
Moreover, in the case of an aforementioned emulsion produced using two liquid catalysts, not only must the two catalysts be mixed together and subjected to self-emulsification at the time of use, but the usable lifetime of the composition also tends to be short. Moreover, in the case of this type of composition, because the overall composition has a three-liquid configuration, the dispersibility of the catalysts within the main emulsion tends to have a significant effect on the properties of the resulting composition.
Patent Document 4 proposes one method for addressing the problems described above, by using an emulsion of a platinum-based catalyst that employs a specific emulsifying agent as the catalyst for a silicone emulsion. However, although there are no particular problems when the amount of Pt used is comparatively large, if the amount of platinum reported in terms of the mass of elemental platinum relative to the total mass of silicone is 100 ppm or less, and particularly 80 ppm or less, then the curability of the composition tends to be unstable.
Although a variety of metals have been proposed for use as the catalyst used in addition reactions, platinum is the most preferred from a practical perspective, and this situation remains unchanged today. However, in recent years, the industrial demands for rare metals such as platinum have continued to increase, and the need to conserve resources means there is much demand for efficient use of these metals. From an economic viewpoint, this increased demand has also caused significant increases in the price of these rare metals, and this trend towards higher prices is particularly marked in the case of platinum. As a result, an addition reaction-curable silicone emulsion that exhibits stable curability even when the required amount of platinum is reduced dramatically has been keenly sought.
[Patent Document 1] U.S. Pat. No. 3,900,617
[Patent Document 2] GB 1599209 A
[Patent Document 3] JP 06-47624 B
[Patent Document 4] JP 08-245887 A